Coating composition and process of making the same



' mospheric oxygen.

Patented I Mar. 20, 1928.

UNETE 3 STATEfi ram car es.

CHARLES H. A. STINE AND COLE COOLIDGE, OF WILMINGTON, DELAWARE, ASSIGNOBS TO E. I. DU PONT DE NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A COB- roaa'rron or DELAWARE.

COATING COMPOSITION AND PROCESS OF MAKING THE SAME.

li'o Drawing.

' This invention relates to coating compo-- sitions or paint and varnish liquids in which rubber is incorporated with an oil, preferably dryingor semi-drying; and has for its object certain improvements in the working properties of such coating compositions.

In co-pending application, Serial No. 681,648, filed December 19, 1923, methods have been disclosed for the preparation of coating compositions or paint and varnish liquids by combining solutions of unvulcanized rubber or caoutchouc with drying oils; therein is also disclosed the fact that films produced from such liquids, either with or without the incorporation of pigments, may be hardened by heating to relatively low temperatures ,for suitable periods of-time; and further that the drying or hardening of such films may be promoted if desired by the incorporation of suitable metallic driers, curing agents, or vulcanizing agents and accelerators. i

We have discovered, however, that when metallic driers are used to bring about rapid hardening of the films obtained therefrom, the preparation of paint. and varnish liquids containing unvulcanized rubber and a drying oil which are satisfactory from a practical standpoint, depends upon a proper understanding of certain relationships which we have found to exist between the amount of met allic. drier present and changes which occur in the bodyor viscosity of such paint and varnish liquids when the latter are allowed to stand more or less exposed to at- If these changes in body or viscosity are not properly controlled, the liquids may in a relatively short time become unsuitable for practical use.

We have observed for example that a paint or varnish liquid containing 100 lbs. of crude rubber, gals. of drying oil carrying an amount of cobalt linoleate equivalent to 0.03% Co (on the basis of weight of oil) and thinned to a consistency satisfactory for paint purposes, will on standing for only two days time with only moderate application of the liquid as a varnish, or of paint or enamel made by the incorporation of pigments therewith, impracticable.

If. in the above combination, the amount of drier be reduced to the equivalent of Application filed September 5, 1924. Serial No. 738,018.

0.01% Co or less (on the basis of oil weight) the rate of change in body or viscosity is reduced to a very marked extent, so much so that after 21 days standing with moderate exposure to atmospheric oxygen, the material is still satisfactory for paint and var-.

of standing:

Table I.

- Viscosit after standin Amount Y 8 Sample No. of drier as y viscosity 2 days 7 days 21 days None. 2. so 2. 2s 2. 25 a a 0. 003 2. 50 2. 30 2. 30 2. 25 0. 005 2. 45 2. 30 2. 30 2. 05 0. 008 2. 30 2. 25 2. 25 I. 95 0. 01 2. 45 2. 25 2. 0 l. 0.03 2.25 1.0 0.5 (0.5

All of the liquids referred to in the above tabulation contained the proportion of 50 gals. of drying oil per 100 lbs. of rubber and were thinned to the initial viscosity with volatile solvent. The drier used was cobalt linoleate, the amount being expressed as Co on the basis-of weight of oil. The determinations. of viscosities were made by the air-bubble test described by Messrs. H. A. Gardner and P. C. Holdt in Circular No. 178 of the Paint Manufacturers Association, using a set of standard tubes obtained from that laboratory. The figures given in the above tabulation represent the approximate absolute viscosities in poises at 25 C. Other well-known methods. could, of course, be used for the determinations of viscosity.

The viscosity tests were made on samples of liquid stored at room temperature in 1 pint friction top paint cans of approxi mately 8cm. diameter X 10 cm. depth internal dimensions, filled to about 75% of .content equivalent to about 0.003 to 0.005%

Co on the basis of weight of oil is to-be preferred for compositions containing the proportion of about gals. of drying oil per 100 lbs. of rubber. The use of even these small amounts of drier results, however, in

a very appreciable improvement in the hard-"' ness and durability of films obtained as compared with those obtained whenno drier is used. The time required for hardening" or drying the film is also materially decreased. In other words, the use of an amount of drier equivalent to about 0.003 to i 0.005% Co on the basis of weight of oil imparts highly desirable properties to these paint and varnish liquids without bringing about to an appreciable extent the undesirable changes in body or viscosity which are.

j encountered when larger amounts of drier are used. In some cases, however, asmuch as the equivalent of 0.01% Coma be employed to advantage, and we have a so found 4 it at times desirable to employ as little as the equivalent of 0.001% Co. In general, however, for paint and varnish liquids con- "taining the proportion of sayabout 40 to gals. of drying oil per 100 lbs. of rubber, we prefer to use from about 0.003 to. 0.005% 00 as cobalt linoleate on the. basis of oil weight. Films prepared from such compositions are preferably dried by heating.

' case of paints or enamels upon the articu-I quired for drying-i depend'upon the-specific at moderate temperatures (say from about to 175 C.) and under such conditionsextremely hard, w'aterproofi durable coatin are obtained. The exact conditions reuse to which the m is to be put, and in the lar pigment or combination of pigments employed. For example, when zinc oxide isthe principal pigment present, drying for" about three hours at 120 (hgives highly. satisfactory results, whereas v when carbon I black is the chief pigment present a higher temperature'of 160 C. is r uired, although the time may be reduced to a out two hours.

We, therefore, do not wish to limit ourselves to any particular conditions under which films obtained according to this invention may be dried.

- We have also prepared paint and varnish liquids containing the proportions of gals. and 100 gals. of drying oil per 100 lbs. of crude rubber (which, following customary varnish. terminology, may be re erred to as pe)ing 75 and 100 gals. oil length respectivey changes in body is analogous to that of the 50 gals. product, except that when say cobalt linoleate is present equivalent to 0.003% G0 on the basis of weight of oil, the weight of metallic drier in proportionto the rubber content of the solutionis increased in exact proportion to the increase in oil length.

The 75 to 100 gals. liquids containing this amount of drier are therefore found to lose body more rapidly than is desirable for practical purposes. This is illustrated by the data in Table II.

Table Gals. I m Viscosity alter standingper mm Sample lb. rubviscosity her 2 days 7 days 26 days 1 50 2. 5o- 2. a0 2. so 2. 25 2 75 2.45 2.25 2. 25 1. 75 a. 100 2.30 2.20 1.05 1.0

Oil in each case contained 00 on basis of weight of oil.

1f the drier content of the longer oil liqulds 1s decreased to such'an extent-that changes in body are no longer serious, the

The behavior of these with respect to eobaltlinoleate equivalent to 0.006%

maximum degree of hardness is not obtained in the dried film, Hence, we have found it expedient to prepare such liquids without the. addition of any drier (or only a very small amount of drier), and to add part or all of the desired amount of drier just prior 1 to or shortly before the use of the liquid for coating purposes. In this manner the difliculties'encountered due to changes in Viscosity ma be overcome, and a larger proortion of rie'r used than would otherwise e feasible. We have, for exam le, found it desirable with liquids of 7'5 an gals. oil length toemploy in this manner up to .the equivalentof say about 0.05%.to 0.1%

Co onthebasis of oil weight.

Similarly we have found that for rubber- 50 gals. oillength, the drier content of the oil may be increased rou hly in inverse prooil compositions of substantially less than portion to' the oil-*lengt that is,-for any given oil length there is a maximum-drier content which maybe employed without resulting in serious changes in viscosity when the liquid is allowed to stand more or less in contact wtih' atmospheric oxygen- For oil lengths of about 50 gals. or less this maximum drier content is usually suflicient to allow the 'obtainment of suitably hard, dura-v ble films when the'proper drying conditions (that is time and temperature) are. em-

.gloyed. It is' obvious. from the foregoing isclosures, however, that, if desired, addrtional drier or driers may be added to such products shortly prior to their use for coating purposes and the material used for such purposes before the lapse of sufficient time in more or less contact with atmospheric oxygen for changes in viscosity to occur to an undesirable extent.

Although in the above discussion we have, for the sake of simplicity, confined our ex amples to the use of cobalt linoleatc as a drier, we have found that other driers behave similarly, although the optimum percentage of different driers varies widely. For example, we have found that as far as the effect on changes in viscosity is concerned, an amount of lead drier containing 0.05% Pb and an amount of zinc drier containing. 0.25% Zn are substantially equivalent in effect to an amount of cobalt drier containing 0.003% Co. lVhat-we have said,

therefore, as applying specifically to cobalt driers also holds more or less generally for other driers, and in the practice of our invention we do not limit ourselves to the use of any particular drier.

We have mentioned the effect of moderate exposure to atmospheric oxygen on the changes in body or viscosity that have been described. We have further observed'thatif paint or vanish liquids as. described'here- 1n, containing various amounts of metallic drier, are preserved out-of contact with oxygen, substantially no change in body occurs; also that even when no metallic drier is present, liquids in contact, with gen lose body slowly- These observations indicate another manner in which our invention may be carried out; .an amount of drier inexcess of that which may be employed without bringing about rapid changes in the body or viscosity atmospheric oxy- (in contact with oxygen) may be'incorporated with coating compositions containing crude rubber and drying oils. The composition may then be preserved out of contact with air or oxygen, say in a sealed container, which will prevent an appreciable change in the viscosity. The composition may then .be opened and employed for coating purposes before the lapse of sufiicient time in contact with atmospheric oxygen forchanges in viscosity to occur to an undesirable extent. The lengthof time which may elapse will, of course, depend upon the amount and kind of drier employed.

The changes in viscosity which. we have observed when compositions containing crude rubber, drying oil and metallic drier are exposed to atmospheric oxygen may be explained on the basis of observations disclosed above, as follows: It is well known that oxygen brings about, more or less slowly, a depolymerization of rubber in solution, the oxygen probably acting catalytically. Since metallic driers are essentially oxygen carriers, it is reasonable to suppose that they the relationships which have been described above between the amount of drier present and changes occurring in the body or viscosity of these liquids, and control of the amount of drier used, in accordance therewith. It will be understood that the scope of the invention is not limited in application to the control of the viscosity of rubber-oil coating compositions when used as such in a manner similar to clear varnishes, but extends also to paints, enamels or color varnishes in which such rubber-oil'compositions are used as a vehicle with suitable pigments or inert materials'incorporated therein.

It is to be understood'also that although the use of crude ornunvulcanized Hevea rubber is preferred in the practice of our invention, we do not wish to limit ourselves to this raw material, as other types of rubber can also be used with advantage, including botanical types, as balata, gutta percha, etc., also partly or wholly vulcanized rubber, including reclaim, etc. In the interpretation of our claims the term rubber is meant to include crude or unvulcan ized caoutchouc, under which head may be included all the botanical varieties such as Hevea, balata, gutta percha etc., and, as well, includes vulcanized rub er of any b0- tanical variety in the state of partial, vulcanization to the state of complete vulcanization, also reclaim, etc. I

The term oil is used to cover animal, vegetable or mineral oils including alltypes as drying, semi-dyring, or non-drying oils,

and as well, especially-treated oils; for ex- .ample, blown 0r ozonized oil's.

avoid heating thev rubber in the mixing operation, or afterwards, to temperatures much above. 300 F. as has been customary in processes heretofore proposed. We have found that when heated to these righ temperatures depolymerization, or other deleterious change in the rubber, apparently occurs.

with the result that films obtained with the rubber-oil combination are apt to remain sticky or tacky on drying, and are not at all durable or practicable as protective or decorative coatings. No such depolymerization occurs, however, if the mixing operation is performed at temperatures of, for example,

1. The process which comprises mixin 10 parts of unvulcanized' rubber dissolve in a rubber solvent with from'about to 50 parts of a drying oil, thinning with a volatile solvent to a suitable consistency 'for coating purposes and incorporating therein an amount of cobalt drier equivalent to from about 0.001% to 0.01% cobalt metal qn the basis of weight of oil used.

' 2. The process which comprise incorporating suitable pigments or inert materials with a composition containing 10 parts of'crude or unvulcanized rubber, from about 30 to 50 parts of a drying oil, a volatile thinner and an amount of cobalt drier equivalentto from about 0.001% to; 0.01% Co on the basis of weight ofoil.

3. Theprocess which comprises mixing 10 parts of unvjulcanized rubber dissolved in a rubber solvent with from, about 30 to 50 parts of a drying oil, thinning with a volatile solvent to a suitable consistency for coating purposes and incorporating therein an amount of metallic drier having, upon exposure to the atmosphere, an effect on the viscosity of the rubber solution equal to that of an amount of cobalt drier equivalent to from about 0.001% to 0.01% cobalt metal on the basis of weight of oil employed.

4. The process which comprises preparing a solution of rubber in a volatile solvent,

said'solution having a suitable consistency.

for use as a coating-composition, and incorporating therein a drying oil and an amount of metallic drier having, upon exposure to the atmosphere an effect on the viscosity of the rubber solution equal to that voffan amount of cobalt drier equivalent to from about 0.001%. to 0.01% cobalt metal on th basis of weight of oil employed.

5. The process which comprises incorporating-suitable pigments or inert materials with a composition containing 10 parts of crude or unvulcanized rubber, from about '30 to parts of a drying oil, a volatile thin ner and an amount of drier. having,".u'pon exposure to the atmosphere, an efl'ect on the,

' viscosity of the rubber solution equal to that of an amount of cobalt drier equivalent to from about 0.001%to 0.01% cobalt metal on the basis of weight of oil employed.

6. The process which comprises mixing 10 parts ,of unvulcanized rubber dissolved in a rubber solvent with from about 3.0 to '80 partsof a drying oi], thinning with a volatile solvent to a suitable consistency for coating purposes and incorporating therein an amount of cobalt drier equlvalent to from about .001% to .0l% cobalt metal on m alent to the basis of weight of oil used, whereby, with exposure to atmospheric oxygen ordinarily encountered in the art, the viscosity of the composition remains satisfactory for coating purposes over a period of time in excess of two days, 1

7. The process which comprises incorporating suitable pigments or inert materials with a composition containing 10 parts of crude or unvulcanized rubber, from about 30 to 80 parts of a drying oil, a volatile thinner and. an amount of cobalt drier equivalent to from about 001% to .01% cobalt on the basis of weight of oil whereby, with exposure to atmospheric oxygen ordinarily encountered in the art, the viscosity .of the composition remains satisfactory for coating purp'oses-over-a period of time in excess of two days. a

8. The process as defined in'claim 6, in which process the mixture comprising-rub:

her and oil is maintained at a temperaturefbelow 200 F.

- 9. A coating composition comprising 10 parts of unvulcanizedrubber, about 30 to 50 parts of a drying oil, a volatile solvent and an amount of metallic drier having,

10. A coating composition comprising a I solution of rubber in a rubber solvent, a drying oil'and an amount of metallic drier having, upon exposure to the atmosphere, an effect on the viscosity of the rubber solution equal to that of anamount of cobalt drier equivalent to from about 0.001% to 0.01% cobalt metal on the basis-of weight of oil employed. 5 1 1. A coating composition comprising a solution of rubber in a rubber solvent, a dryoil and an amount of cobalt drier equivfrom about 0.001% to 0.01% cobalt metal on the basis of weight of oil employed.

12. The process of making a coating comosition which comprises mixing unvulcanlzed rubber, a drying oil, and ametal drier, in the proportions of more than 40 gallons -of oil for each pounds of rubber, the amount of drier used-being equivalentto between 0.001 a'ndl0.01% of cobalt based on the weight of oil, said rubber and oil being mixed ata temperature below 200 F.

13. The process'which comprises dispers- 'ing' unvulcani zed rubber" in a drying oil, mixmg therewith an amount of a metal drier to a temperature room temperature to about 14. The process which comprises heating,

in the form of a thin film, a mixture con-.

taining a pigment, a thinner, a drying oil and unvulcanized rubber in the proportions of from 40 to 100 gallons of oil to each 100 poundsof rubber, and a metal drier equivalent to between 0.001 and 0.01% of cobalt based on the weight of oil present, to a temperature between about and 175 0., to volatilize the thinner, oxidize the oil, and cure therubber. I

15. The process which comprises subject ing, inthe form of a film, a mixture contaming unvulcanized rubber, a drying oil in the proportion of from-40 to gallons of oil toeach 100 pounds of rubber, and from of a metal drier, based on the combined weight of rubber and oil present,

C1 in the presence of air until the oil has become oxidized and the rubber cured to the desired degree.

between 0.001% and 0.01%

of from about ordinary 16. A coating composition comprising a mixture of unvulcanlzed rubber, a. drying oil, a metal drier and a thinner, there being more than 0.4 gallon of oil for each pound of rubber in the mixture.

17. A coating composition comprising incompletely vulcanized rubbe1','a drying oil, a metal drier, a thinner, and a special curing agent for the rubber, from 0.4 to 10 gallons ofoil being used for each pound of rubber, and the amount of drier being equivalent to of cobalt based on the weight of oil present.

, 18 A coating composition in the form of a hard, durable film comprising cured rub-- ber dispersed throughout a drying oil containing from about 0.001% and 0.01% of its weight of cobalt.

.In testimony whereof we afiix our signatures.

CHARLES M. A. STINE. COLE COOLIDGE. 

